Position-insensitive mercury relay

ABSTRACT

A miniature mercury switch, comprising an enclosure including a tube having a mercury wettable inner surface, within which a contact carrying shuttle is movable along the axis of the tube. The shuttle is not mercury wettable except for a slot or groove extending between its ends and for contact surfaces at its ends, but it rides on a mercury layer attached to the inner surface of the tube. Secured within and extending into the ends of the tubes are unwettable rods of magnetic material having stationary end contacts which are mercury wettable. The contacts on the shuttle ends include tantalum or niobium spacers extending beyond mercury wettable end contact surfaces on the shuttle, the spacers accepting the impacts when the relay contacts operatively close, which implies that the wettable contact areas on the shuttle ends closely approach the stationary end contacts, so that the mercury layers coalesce, but the wettable surfaces do not impact. The quantity of mercury within the enclosure is only sufficient to form a layer of mercury on the mercury wettable surfaces within the enclosure, but insufficient to form a pool of mercury, or to cover unwettable surfaces while wettable surfaces are covered, and the slot or groove in the shuttle facilities transfer or mercury from end to end of the enclosure, which prevents pooling at either end of the enclosure concomitant with depletion at the other, due to imbalance of mercury transfer during relay operation. Stationary contacts are, for open contact condition, spaced from movable contacts, by mercury unwettable surfaces of the enclosure, and the quantity of mercury available is insufficient to cover these unwettable surfaces and also to form a mercury layer on the mercury surfaces.

United States Patent [191 Bitko Feb. 18, 1975 POSITION-INSENSITIVE MERCURY RELAY [75] Inventor: Sheldon S. Bitko, Cherry Hill, NJ. 7

['73] Assignee: Fifth Dimension lnc., Princeton, NJ;

[22] Filed: Oct. 19, 1973 21 Appl. No.: 407,899

Related U.S. Application Data Division of Ser. No. 302,677, Nov. 1, 1972, Pat. No. 3,786,217, which is a continuation-in-part of Ser. No. 880,128, Nov. 26, 1969, Pat. No. 3,644,693.

Primary Examinerl-lerman J. Hohauser Attorney, Agerzz, 0r Firm-l-lyman l-lurvitz [5 7] ABSTRACT A miniature mercury switch, comprising an enclosure including a tube having a mercury wettable inner surface, within which a contact carrying shuttle is movable along the axis of the tube. The shuttle is not mercury wettable except for a slot or groove extending be tween its ends and for contactsurfaces at its ends, but it rides on a mercury layer attached to the inner surface of the tube. Secured within and extending into the ends of the tubes are unwettable rods of magnetic material having stationary end contacts which are mercury wettable. The contacts on the shuttle ends include tantalum or niobium spacers extending beyond mercury wettable end contact surfaces on the shuttle, the spacers accepting the impacts when the relay contacts operatively close, which implies that the wettable contact areas on the shuttle ends closely approach the stationary end contacts. so that the mercury layers coalesce, but the wettable surfaces do not impact. The quantity of mercury within the enclosure is only sufficient to form a layer of mercury on the mercury wettable surfaces within the enclosure, but insufficient to form a pool of mercury, or to cover unwettable surfaces while wettable surfaces are covered, and the slot or groove in the shuttle facilities transfer or mercury from end to end of the enclosure, which prevents pooling at either end of the enclosure con- I the enclosure, and the quantity of mercury available is insufficient to cover these unwettable surfaces and also to form a mercury layer on the mercury surfaces.

2 Claims, 6 Drawing Figures MERCURY 7 were POSITION-INSENSITIVE MERCURY RELAY This is a division, of application Ser. No. 302,677, filed Nov. 1, 1972 now US. Pat. No. 3,786,217 which is a continuation-in-part of Bitko, Ser. No. 880,128, filed Nov. 26, 1969 now US. Pat. No. 3,644,693 entitled: NON-STICKING RELAY CONTACTS, assigned to the assignee of this application.

BACKGROUND OF THE INVENTION This invention is an improvement of the relay disclosed in U. S. Pat. No. 3,144,533, to Donath, issued Aug. 11, 1964. That patent includes a non-wettable shuttle riding on a layer of mercury sustained by the inner mercury wettable surface of a metallic tube. The contacts of the relay are mercury wettable, one at each end of the tube, each contact coacting with mercury wettable contacts formed on the ends of the shuttle. It is found that after long shelf life or many closures of the Donath switch the contacts of the Donath relay tend to stick, the numbers of trouble-free operations decreasing with increase of temperature. Study of the mechanism of sticking indicates that it is caused by diffusion of metal between contacts due to promimity or current flow, and that this occurs despite the mercury layers on the contacts and perhapsbecause of it, since mercury wettablemetal tends to be soluble in mercury. All attempts to discover metals which while mercury wettable and therefore suitable as contacts, are also totally non-soluble and non-transferable under proximity or current flow were unsuccessful.

The concept was then advanced of including in each of the shuttle contacts an impact absorbing spacer which is non-mercury wettable, and hence not soluble in mercury, but sufficiently hard to absorb impact without substantial deforinationThe contacts themselves must be wettable, but these are located so far inward of the spacers that a mercury layer attached to the shuttle contact can reach the mercury layer attached to the stationary contact, yet are so located that no impact or transfer of metal occurs between the mercury wettable surfaces. This concept is broadly disclosed and claimed in Bitko, Ser. No. 880,l28,'supra, as applied to a reed switch or relay. The present invention relates to the same broad concept as does Ser. No. 880,128, but applied to a shuttlerelay, and includes novelty in respect to the fabrication and structure of the shuttle. The en- 1 velope is designed to permit of particularly economical assembly from simple parts.

SUMMARY OF THE INVENTION A mercury relay having a shuttle armature riding on a thin layer of mercury, in which the ends of the shuttle are mercury wettable but provided with non-mercury wettable projections which provide spacing to stationary contacts and thus prevent contact sticking.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a new partly in side elevation and partly in section of a relay according to the invention;

FIGS. 2-5 are sections taken through a solid cylinder of material at various stages in the fabrication of a shuttle for the relay of FIG. 1;

FIG. 6 is a broken away view in side elevation illustrating details of contacts of the relay of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The relay of FIG. 1 is provided with two stationary contact bearing rods 1 and 2, the contacts being stationary and extending into a sealed envelope 3. Rods l and 2 are fabricated of non-mercury wettable magnetic material but each end surface is provided with a coating r layer 4 of mercury wettable or such as platinum. The thickness of the coating or layer may be about 0.0002 inch. The rod must be relatively hard, to withstand repeated impacts without deformation, but the coating or layer may be relatively soft, and therefore may suffer deformation.

A glass annulus 5 surrounds each rod interiorly ofthe envelope at its ends, and is sealed thereto, providing insulative support.

Interiorly of the envelopes is a thin walled metallic tube 6 of circular cross section, which is metallic and interiorly mercury wettable. From the tube, midway thereof extends an annulus 7, which serves to position actuating coils 8, 9 and also to position two glass cylinders 10, 11 which extend over tube 6 from opposite ends and extend beyond the tube 6 at each end of the tube 6, into superposed conjunction with glass annulus 5. The glass tubes 10, 11 are heated to effect a seal with the metallic tube 6 and with the glass annuli 5 and with the metallic annulus 7, and theenclosure is further end sealed by discs 12. Thereby. an enclosure is formed, which is hermetically sealed so that it may be filled with inert gas.

Within the enclosure is located a shuttle 14, having thereon a helical groove 15 extending along the entire length of the shuttle. The shuttle 14 is generally cylindrical in outline as seen from its end and presents a sliding fit within the tube 6, making allowance for a thin layer of mercury 16 intervening between the shuttle and the tube. Theouter surface layer 17 of the shuttle is not mercury wettable. The helical groove 15 extends into a non-magnetic but mercury wettable core 18, and a tantalum or niobium tube 20, which is not wettable, extends between the outer layer of the shuttle andthe inner core. The groove'provides a path for interchange of mercury between the ends of the envelope, which is required to assure balanced distribution of mercury, at least statistically. If the groove is not provided, mercury may collect in one side of the switch, resulting in a short at that side and possible dry contacts on the other side. The groove also conveys mercury which is integral with or joined with that existent in the thin layer on the tube 6, thereby to provide a low resistance path directly from the core 18 of the shuttle to the outer tube.

The shuttle requires, at each of its ends according to 6O movable contact surface 22, which is mercury wettable the present invention, an interposer 21 between the contact surface 22 by about one mil. While the interposer 21 may be fabricated in a variety of ways, a preferred way is to remove an annulus 25 of the outer end of tube 21, exposing a ring of the interposer metal, and thereafter exposing the interposer metal to a hot hydrogen atmosphere. This treatment causes the interposer metal, if tantalum or niobium, to expand by absorption of hydrogen. However, it is also feasible to remove a layer, of metal from the core 15, as by dissolving it in hotmercury. ln either case, the interposer is produced as a projecting annulus, which impinges against the contact surface 19 when the contacts close. The interposer metal, being mercury non-wettable, cannot diffuse into the mercury. The layer 19 is relatively soft, and quite thin, while the interposer is relatively hard, so that relatively few operations of the relay produce an annular recess 26, extending through the layer 4. The interposer 21 is slightly longer axially than the recess 26 is deep, so that the interposer always impinges directly on the end of rod 1, which is itself not mercury wettable. Thereby, the metal layer 4 does not diffuse on impact, and the relay is free of sticking, indefinitely.

A preferred method of fabricating the slug 14 is to start with a cylinder 29 comprising a non-magnetic, mercury wettable core 16, interiorly, an inner tube of tantalum 20, surrounding core 16, and an outer tube of magnetic, non-mercury wettable metal 17, all integral with one another. The cylinder 29 is flattened by rolling, as illustrated in FIG. 3, and cut down along the line 30, as by grinding, to expose the inner core 18, resulting in an elongated member'which is generally ovoid for more than half its circumference and flat for the remainder, the flat surface 31 exposing all three metals. The shape of FIG. 4 is further rolled to achieve precise dimensions and the resultant shape is twisted to form a multi-turn helix, which can be electropolished to precise OD and length dimensions, and to have an essentially circular outline as viewed from an end.

The present relay has the operating properties of the Donath relay, plus the additional property that its contacts do not stick even after many millions of closures. Particularly, it may be mentioned that the switch is inherently bistable, and can therefore be operated in response to a short impulse which need not endure.

The wettable to non-wettable surface ratio of the Donath switch is substantially retained and the OD, length and general operating characteristics may re main as described in The Donath patent, to which ref erence is made for a complete discussion of the theory and philosophy of operation.

The helical shuttle or slug 14 should preferably be symmetrical in respect to weight distribution along its length and also in respect to distribution of strip 15, which because it is wettable establishes a drag, and also in respect to the outermost non-wettable surface. The first mentioned objective, i.e., symmetry, is readily achieved by having a helix of an integral number of turns, in the present case, two. Reduction of the area i of the non-wettable surface reduces friction, and controlling the depth and width of the inner diameter of 15 of the helix, which is mercury wettable, affects total shuttle mass, because mercury is dragged along the shuttle, The presently described method of making the shuttle enables ready control of the several factors mentioned. There is a problem of so proportioning the dimensions of the shuttle that it is magnetically symmetrical and also symmetrical in respect to weight dis tribution, so that on transfer ofthe shuttle from one location to another it will ride axially and this in any orientation of the relay, which is totally position insensitive. This is accomplished by employing an integral number of helical turns, and conformity of structure along the length of the slug.

It will be appreciated that core 15 need not be nonmagnetic.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

I claim:

1. A mercury switch comprising:

a mercury wettable metallic tube,

a slug located internally of said tube,

a quantity of mercury located internally of said tube,

said slug floating in said mercury and movable longitudinally of said tube,

a mercury unwettable insulating ring terminating said tube at one end,

said slug being mercury wettable at its end nearest said one end, the total length of said slug being at least as great as the total internal length of said tube,

wherein said slug includes a central elongated core of mercury wettable material substantially surrounded by a layer ,of metal selected from the group tantalum and niobium, in turn surrounded by a layer of non-mercury wettable magnetic material, said layer of metal projecting axially beyond the confines of said core and said layer.

2. In combination,

a shuttle floating in a layer of mercury,

a mercury wettable element confining said mercury and said shuttle,

said shuttle having a mercury unwettable surface in contact with said mercury,

a channel extending along the length of said shuttle and having mercury unwettable walls, wherein said shuttle includes a central elogated core of mercury wettable material,

a layer of metal selected from the group tantalum and niobium essentially surrounding said core, and

a layer of magnetic material essentially surrounding said layer of metal,

ers to said core. 

1. A MERCURY SWITCH COMPRISING: A MERCURY WETTABLE METALLIC TUBE, A SLUG LOCATED INTERNALLY OF SAID TUBE, A QUANTITY OF MERCURY LOCATED INTERNALLY OF SAID TUBE, SAID SLUG FLOATING IN SAID MERCURY AND MOVABLE LONGITUDINALLY OF SAID TUBE, A MERCURY UNWETTABLE INSULATING RING TERMINATING SAID TUBE AT ONE END, SAID SLUG BEING MERCURY WETTABLE AT ITS END NEAREST SAID ONE END, THE TOTAL LENGTH OF SAID SLUG BEING AT LEAST AS GREAT AS THE TOTAL INTERNAL LENGTH OF SAID TUBE, WHEREIN SAID SLUG INCLUDES A CENTRAL ELONGATED CORE OF MERCURY WETTABLE MATERIAL SUBSTANTIALLY SURROUNDED BY A LAYER OF METAL SELECTED FROM THE GROUP TANTALUM AND NIOBIUM, IN TURN SURROUNDED BY A LAYER OF NON-MERCURY WETTABLE MAGNETIC MATERIAL SAID LAYER OF METAL PROJECTING AXIALLY BEYOND THE CONFINES OF SAID CORE AND SAID LAYER.
 2. In combination, a shuttle floating in a layer of mercury, a mercury wettable element confining said mercury and said shuttle, said shuttle having a mercury unwettable surface in contact with said mercury, a channel extending along the length of said shuttle and having mercury unwettable walls, wherein said shuttle includes a central elogated core of mercury wettable material, a layer of metal selected from the group tantalum and niobium essentially surrounding said core, and a layer of magnetic material essentially surrounding said layer of metal, said channel being a slot extending through said layers to said core. 